Manufacturers of compression-ignition engines incorporate exhaust aftertreatment systems to meet requirements of various emissions regulations and to address customer satisfaction issues. Emissions regulations implemented in countries throughout the world include standards for allowable levels of exhaust gas constituents output as a result of combustion of fuel in an internal combustion engine. The primary regulated exhaust gas constituents include hydrocarbons (‘HC’), carbon monoxide (‘CO’), nitrides of oxygen (‘NOx’), and carbon particulate matter (‘PM’). Engine manufacturers meet various emissions regulations by designing engines, engine control systems and exhaust aftertreatment devices to reduce NOx to nitrogen (‘N2’) and oxygen (O2), and oxidize HC, CO, and PM to water (‘H2O’) and carbon dioxide (‘CO2’). Compression-ignition engines operating at lean air/fuel ratios typically have low engine-out emissions of CO and HC, and higher levels of engine-out emissions of NOx and PM.
Engine system designers reduce NOx emissions and PM of compression-ignition engines using several different aftertreatment devices and control schemes. The aftertreatment devices include, for example, NOx adsorber catalysts, diesel particulate filter devices (“DPF”), oxidation and three-way catalysts, and selective catalytic reduction catalysts. The aftertreatment devices are placed in an exhaust gas feedstream for use in conjunction with engine management control schemes to reduce engine-out and tailpipe emissions below regulated levels. Each aftertreatment device typically has a preferred set of operating parameters over which it operates optimally. When the exhaust gas feedstream is outside the optimal range of operating parameters for a specific aftertreatment device, emissions performance may be adversely affected.
Engine system designers implement various systems to ensure the exhaust gas feedstream from the engine is within an optimal range of operating parameters for each aftertreatment device. One system is a delivery system that introduces a supplemental material into the exhaust gas feedstream upstream of the aftertreatment device. Supplemental materials typically include diesel fuel, ammonia (NH3), or aqueous urea. Diesel fuel is injected into the exhaust feedstream to shift the exhaust air/fuel ratio to stoichiometry or rich of stoichiometry. Added diesel fuel in the exhaust causes an exothermic reaction and increased temperature in the aftertreatment system. Increased temperature facilitates regeneration of DPF devices and desulfation of NOx adsorber catalysts. A shift in air/fuel ratio typically facilitates desorption of NOx from a catalyst surface, and leads to conversion to nitrogen (N2), oxygen (O2), and water (H2O). Ammonia or aqueous urea is injected into the exhaust feedstream to enhance and improve conversion of NOx to N2 in a selective catalyst reduction device.
A system for delivering supplemental material to an exhaust gas feedstream typically comprises an injecting device, a fluid delivery system, and an air pressurizing system. The fluid delivery system typically comprises a fluid reservoir containing supplemental material and a fluid conduit for delivering the supplemental material to the injecting device. The air pressurizing system typically comprises an air pump or air compressor whose output is connected to the injecting device. An injecting device typically comprises a metering device wherein the pressurized air from the air pump and the supplemental material are mixed and delivered to a nozzle placed in the exhaust system for dispersal into the exhaust gas feedstream.
An internal combustion engine may be described as an air-pumping device, wherein fresh air is drawn into the engine through an intake system and pushed out through the exhaust system. Backpressure is a term that describes resistance to airflow through the exhaust system. The magnitude of backpressure increases as components are added to the exhaust system for emissions control and noise abatement. Designers must understand and accommodate a range of backpressure levels over the entire range of engine operation when determining operating requirements for a delivery system for supplemental materials. The air pressurizing system of the delivery system must effectively pressurize the delivery system at high speed, high load, and high exhaust backpressure conditions and at low speed, low load, and low exhaust backpressure conditions. Designers have proposed air pressure systems that incorporate a conventional turbine-style pump to pressurize the air for use with the delivery system. However, a typical turbine-style pump may lack the dynamic range and capacity to deliver sufficient level of air pressure and flow of supplemental material at high speed, high load, and high backpressure conditions. Designers have proposed the use a high-pressure, positive-displacement pump with capacity to operate over the entire range of backpressure for a given system. A high-pressure, positive-displacement pump typically adds significant cost, mass and power consumption to a system, and is rarely used at its maximum capacity.
Therefore, what is needed is a pump for an air pressuring system for a system that delivers supplemental material to an exhaust gas feedstream that is capable of meeting the performance requirements for high speed, high load, and high backpressure operation, without incurring the costs associated with a high-pressure, positive-displacement pump.